The present invention relates to an electromagnetic brake and, more particularly, to an excitation type electromagnetic brake for applying brake to a rotating shaft of a motor or the like via a magnetic fluid and a non-excitation type electromagnetic brake which incorporates a permanent magnet and performs braking action via a magnetic fluid. In this specification, the motor is not limited to an electric motor, and includes a motor and the like having a rotating shaft which are driven by a fluid pressure such as an oil pressure or an air pressure.
For example, an excitation type electromagnetic brake as shown in FIG. 8 has conventionally been used for the motor of this type.
Referring to FIG. 8, an excitation type electromagnetic brake 201 includes an electromagnetic brake body 203 which is mounted on a case (hereinafter referred simply to as a case) 202a integrated with a stator of an electric motor 202 and having a yoke member 205 with an exciting coil winding 204, and an armature 206 serving as a brake movable member fixed to a motor rotating shaft 202b by a fixing member 207 via a leaf spring 208. The armature 206 is designed so as to be capable of moving in the axial direction by an amount of deflection of the leaf spring 208. Reference numeral 209 denotes a rectifier circuit section.
When the exciting coil winding 204 is excited, the electromagnetic brake body 203 is operated. Specifically, the armature 206 is attracted toward the yoke member 205 against the urging force of the leaf spring 208, and comes into direct contact with the yoke member 205 or comes into contact with a friction plate, not shown, fixed to the yoke member 205. Therefore, a braking force is created by friction, so that the rotation of the rotating shaft 202b is stopped.
When the exciting coil winding 204 is not excited, the armature 206 is separated from the electromagnetic brake body 203 by the urging force of the leaf spring 208, so that the rotating shaft 202b is released from the brake.
However, the conventional excitation type electromagnetic brake 201 having a construction as described above has the following problems because braking action is performed by the friction:
(1) The braking force is changed by the condition of contact face of the yoke member 205 or the change in surface condition of the friction plate with passage of time, and the service life of brake is impaired by friction. Also, the condition of the friction surface changes with passage of time, so that the brake characteristics are unstable.
(2) When the armature 206 is attracted, there is produced a noise due to the contact of the armature 206 with the yoke member 205 on the electromagnetic brake body 203 side, and also there is produced a noise due to friction at the time of braking.
(3) Since there is an air gap in a magnetic path in which the electromagnetic brake body 203 produces an attracting force, it is necessary to consider the balance between the attracting force and the urging force of the leaf spring 208.
(4) The design of magnetic circuit is very complex; for example, the adjustment of the air gap is delicate.
(5) The braking force is determined by the coefficient of friction of the above-mentioned friction, and it is very difficult to adjust the attracting force of the electromagnetic brake body 203 in the range in which attraction can be effected. Therefore, it is difficult to control the braking force.
On the other hand, for example, a non-excitation type electromagnetic brake as shown in FIG. 9 has conventionally been used for the motor of this type.
Referring to FIG. 9, an electromagnetic brake 211 includes a brake disc 212 serving as a brake movable member, which is fixed to an output rotating shaft 214 of a motor 213, an electromagnetic brake body 215 having a yoke member 217 on the stator side with a coil winding 216, an armature 218 integrated with a brake lining material 218a, and a spring 219 which urges the armature 218 in the direction in which the armature 218 is separated from the electromagnetic brake body 215 to operate the brake. (The brake lining material 218a is sometimes integrated with the brake disc 212.)
When the coil winding 216 is not energized, the armature 218 is separated from the electromagnetic brake body 215 by the urging force of the spring 219, and the brake lining material 218a affixed to the armature 218 is brought into contact with the brake disc 212. Thereby, a braking force is produced by friction, and thus brake is applied to the output rotating shaft 214 of the motor 213.
Also, when the coil winding 216 is energized, the armature 218 is attracted to the electromagnetic brake body 215 against the urging force of the spring 219, and the brake lining material 218a is separated from the brake disc 212, by which the rotating shaft 214 is released from the brake.
In this electromagnetic brake 211, two or more pins 220 are erectly provided on the yoke member 217, and the pins 220 are engaged with pin holes 218b formed in the armature 218, by which the armature 218 is prevented from rotating together with the brake disc 212, and is guided slidably in the direction of the rotating shaft.
However, the conventional non-excitation type electromagnetic brake 211 constructed as described above has problems in that the brake force is changed by the change in surface condition of the brake lining material 218a with passage of time, and the service life of brake is impaired by the friction of the brake lining material 218a, and that there is produced a noise due to friction at the time of braking, and also when the armature 218 is attracted due to excitation, there is produced a noise due to the contact of the armature 218 with the yoke member 217 on the electromagnetic brake body 215 side.
Furthermore, since the armature 218 has a backlash in the direction of rotation, the rotating shaft 214 has a play when being held by the electromagnetic brake 211.
In particular, the electromagnetic brake 211 has problems in that there is a degree of (a non-negligible degree of) air gap in a magnetic path in which the electromagnetic brake body 211 produces an attracting force at the time of excitation, so that it is necessary to consider the balance between the attracting force and the urging force of the spring 219, and that the design of magnetic circuit is very complex; for example, the adjustment of the air gap is delicate.
The present invention has been made in view of the above situation, and accordingly an object thereof is to provide an excitation type electromagnetic brake and a non-excitation type electromagnetic brake in which the above problems are solved, wear of the braking portion is eliminated, whereby the service life thereof can be prolonged, and also a noise produced by the braking portion can be eliminated.
Another object of the present invention is to provide an excitation type electromagnetic brake and a non-excitation type electromagnetic brake in which regarding the construction, in brake application, a movable portion is eliminated, so that the construction can be made simple, and also the number of parts can be decreased.
To achieve the above objects, the present invention provides an electromagnetic brake comprising an electromagnetic brake body having a yoke member with a coil winding and a brake movable member formed of a magnetic material, which is disposed via an air gap in a magnetic path formed by the electromagnetic brake body and is fixed to a rotating shaft, wherein a magnetic fluid is interposed or filled in the air gap, and fluid leakage preventive means is formed or disposed between the electromagnetic brake body and the brake movable member to prevent the magnetic fluid from leaking to the outside, whereby the rotating shaft is braked using the electromagnetic brake when the coil winding is excited.
In the electromagnetic brake, the fluid leakage preventive means is a sealing member, and the sealing member for rotatably sealing the rotating shaft is disposed to prevent the magnetic fluid from leaking from between the electromagnetic brake body and the rotating shaft.
In the electromagnetic brake, the brake movable member is a disc fixed at the end of the rotating shaft.
Also, the present invention provides an electromagnetic brake comprising an electromagnetic brake body having a yoke member with a coil winding so that a rotating shaft is disposed via an air gap in a magnetic path formed by the electromagnetic brake body, wherein a magnetic fluid is interposed or filled in the air gap, and a sealing member for rotatably sealing the rotating shaft is disposed to prevent the magnetic fluid from leaking from between the electromagnetic brake body and the rotating shaft, whereby the rotating shaft is braked using the electromagnetic brake when the coil winding is excited.
Also, the present invention provides an electromagnetic brake comprising an electromagnetic brake body having a yoke member with a coil winding, a brake movable member formed of a magnetic material, which is fixed to a rotating shaft, and a permanent magnet disposed in a magnetic path formed by the electromagnetic brake body and the brake movable member, wherein a magnetic fluid is interposed or filled between the electromagnetic brake body and the brake movable member, and the direction of magnetic force in the excited state of the electromagnetic brake body is made reverse to the direction of magnetomotive force of the permanent magnet, whereby the brake of the rotating shaft is released using the electromagnetic brake, and braking action is performed in a non-excitation state.
In the electromagnetic brake, the permanent magnet is disposed on the brake movable member side.
In the electromagnetic brake, the permanent magnet is disposed on the electromagnetic brake body side.
In the electromagnetic brake, an air gap is formed in a portion between the electromagnetic brake body and the brake movable member in which the magnetic fluid is filled.
Also, the present invention provides an electromagnetic brake comprising a guide rail formed of a magnetic material; an electromagnetic brake body having a yoke member with a coil winding, which is mounted on a carriage formed of a non-magnetic material; and a permanent magnet disposed on the electromagnetic brake body in a magnetic path formed by the electromagnetic brake body and the guide rail, the carriage on which the electromagnetic brake body is mounted being disposed on the guide rail via a roller so as to be capable of running, wherein a magnetic fluid is interposed between the electromagnetic brake body and the guide rail, and the direction of magnetic force in the excited state of the electromagnetic brake body is made reverse to the direction of magnetomotive force of the permanent magnet, whereby the electromagnetic brake is released, and braking action is performed in a non-excitation state.
The magnetic fluid used in the present invention is a colloidal fluid in which ferromagnetic powder (for example, fine particles of about 10 nm) is stably dispersed into a solution (for example, mineral oil, silicone oil, and other oils or water as well as organic solvent). This fluid is chained by magnetism and is made in a solid form or in a fixed state. Even if a shearing force higher than an allowable value acts, the chain of fluids merely separates, and the magnetic powder itself is not affected.
Since the electromagnetic brake in accordance with the present invention is constructed as described above, the magnetic fluid produces a resistance to shearing caused by a fixed chain in a fixed magnetic field, and even after being sheared, it produces a fixed resistance. The resistance at this time can be adjusted by the intensity of magnetic field, and can be made higher than the brake frictional force. Therefore, the whole of the electromagnetic brake can be made smaller in size, and also there is no friction because the electromagnetic brake has no friction parts, which leads to a long service life.
Also, since an armature, which is a conventional movable part, is not needed, no noise is produced at the time of brake application.
Also, in the non-excitation type electromagnetic brake of the present invention, a direct current is caused to flow, and the intensity of magnetic field is adjusted so that a minute magnetic field remains in the magnetic path in order to prevent the magnetic fluid from leaking to the outside when the electromagnetic brake body is excited to release the brake. In this case, the configuration should be such that the action of the magnetic field due to the remaining minute magnetic field does not provide a load on the rotating shaft during rotation. In the case where the action of the magnetic field due to the remaining minute magnetic field is not negligible as a load on the rotating shaft during rotation, a coating for preventing the magnetic fluid from leaking is applied to make the minute magnetic field zero.
Since there is basically no air gap in the magnetic path of the electromagnetic brake in accordance with the present invention, the magnetic resistance can be decreased, and the magnetism design can be simplified.
Also, in comparison with the conventional electromagnetic brake, in the electromagnetic brake in accordance with the present invention, there is no movable part such as a leaf spring, return spring, and armature, so that the construction can be simplified, and the number of parts can be decreased.
For the electromagnetic brake in accordance with the present invention, fundamentally, a subject to which the brake is applied is not limited to a rotating shaft, and in construction, the present invention can be applied to a linear mechanism.
As is apparent from the above description, according to the electromagnetic brake in accordance with the present invention, wear of the braking portion is eliminated, whereby the service life thereof can be prolonged, and also a noise produced by the braking portion can be eliminated.
Also, according to the present invention, there can be achieved an effect that in brake application, a movable portion is eliminated, so that the construction can be made simple, and also the number of parts can be decreased.
Further, since the shearing force of the magnetic fluid can take a larger value than that of friction, the brake itself can be made smaller.
In addition, the shearing force of the magnetic viscous fluid is stable with respect to the rotational speed of the motor rotating shaft and ambient temperature, so that a stable electromagnetic brake can be provided. Further, the current flowing in the exciting coil winding of the electromagnetic brake body can be regulated to control the braking force freely.